linux-kernel - [RFC PATCH] tracing: change syscall number type in struct syscall_trace

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Message-ID: <20231002135242.247536-1-asavkov@redhat.com>
Date:   Mon,  2 Oct 2023 15:52:42 +0200
From:   Artem Savkov <asavkov@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        linux-rt-users@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Artem Savkov <asavkov@...hat.com>
Subject: [RFC PATCH] tracing: change syscall number type in struct syscall_trace_*

linux-rt-devel tree contains a patch that adds an extra member to struct
trace_entry. This causes the offset of args field in struct
trace_event_raw_sys_enter be different from the one in struct
syscall_trace_enter:

struct trace_event_raw_sys_enter {
        struct trace_entry         ent;                  /*     0    12 */

        /* XXX last struct has 3 bytes of padding */
        /* XXX 4 bytes hole, try to pack */

        long int                   id;                   /*    16     8 */
        long unsigned int          args[6];              /*    24    48 */
        /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
        char                       __data[];             /*    72     0 */

        /* size: 72, cachelines: 2, members: 4 */
        /* sum members: 68, holes: 1, sum holes: 4 */
        /* paddings: 1, sum paddings: 3 */
        /* last cacheline: 8 bytes */
};

struct syscall_trace_enter {
        struct trace_entry         ent;                  /*     0    12 */

        /* XXX last struct has 3 bytes of padding */

        int                        nr;                   /*    12     4 */
        long unsigned int          args[];               /*    16     0 */

        /* size: 16, cachelines: 1, members: 3 */
        /* paddings: 1, sum paddings: 3 */
        /* last cacheline: 16 bytes */
};

This, in turn, causes perf_event_set_bpf_prog() fail while running bpf
test_profiler testcase because max_ctx_offset is calculated based on the
former struct, while off on the latter:

  10488         if (is_tracepoint || is_syscall_tp) {
  10489                 int off = trace_event_get_offsets(event->tp_event);
  10490
  10491                 if (prog->aux->max_ctx_offset > off)
  10492                         return -EACCES;
  10493         }

This patch changes the type of nr member in syscall_trace_* structs to
be long so that "args" offset is equal to that in struct
trace_event_raw_sys_enter.

Signed-off-by: Artem Savkov <asavkov@...hat.com>
---
 kernel/trace/trace.h          | 4 ++--
 kernel/trace/trace_syscalls.c | 7 ++++---
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 77debe53f07cf..cd1d24df85364 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -135,13 +135,13 @@ enum trace_type {
  */
 struct syscall_trace_enter {
 	struct trace_entry	ent;
-	int			nr;
+	long			nr;
 	unsigned long		args[];
 };
 
 struct syscall_trace_exit {
 	struct trace_entry	ent;
-	int			nr;
+	long			nr;
 	long			ret;
 };
 
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index de753403cdafb..c26939119f2e4 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -101,7 +101,7 @@ find_syscall_meta(unsigned long syscall)
 	return NULL;
 }
 
-static struct syscall_metadata *syscall_nr_to_meta(int nr)
+static struct syscall_metadata *syscall_nr_to_meta(long nr)
 {
 	if (IS_ENABLED(CONFIG_HAVE_SPARSE_SYSCALL_NR))
 		return xa_load(&syscalls_metadata_sparse, (unsigned long)nr);
@@ -132,7 +132,8 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
 	struct trace_entry *ent = iter->ent;
 	struct syscall_trace_enter *trace;
 	struct syscall_metadata *entry;
-	int i, syscall;
+	int i;
+	long syscall;
 
 	trace = (typeof(trace))ent;
 	syscall = trace->nr;
@@ -177,7 +178,7 @@ print_syscall_exit(struct trace_iterator *iter, int flags,
 	struct trace_seq *s = &iter->seq;
 	struct trace_entry *ent = iter->ent;
 	struct syscall_trace_exit *trace;
-	int syscall;
+	long syscall;
 	struct syscall_metadata *entry;
 
 	trace = (typeof(trace))ent;
-- 
2.41.0